Extracellular Matrix Degradation and Mechanical Integrity of Degenerated Human Annulus Fibrosus from Surgical Specimens

Intervertebral disc (IVD) degeneration is a leading cause of low back pain, yet the mechanistic link between biochemical matrix degradation and functional mechanical failure of the annulus fibrosus (AF) remains poorly defined in human tissue. The interlamellar matrix (ILM), which binds adjacent collagen lamellae via cross-bridges, is a key determinant of AF mechanical integrity, but whether its weakening is driven by aging, pathology, or both and whether this weakening is linked to proteinase-mediated extracellular matrix (ECM) degradation, has not been established. This thesis tested the hypothesis that age-related and pathological IVD degeneration are associated with reduced AF mechanical properties, and that this deterioration is linked to ECM proteolysis. An integrated, multimodal approach combining interlamellar peel mechanical testing, Western blotting, and immunohistochemistry (IHC) was applied to paired human AF samples spanning four groups: Young Asymptomatic, Older Asymptomatic, intervertebral disc degeneration (IVDD), and degenerative scoliosis (dScoli). Peel testing revealed that ILM stiffness, strength, and toughness declined progressively with age in asymptomatic, radiographically normal donors, with the most pronounced deterioration occurring in the fifth decade of life — demonstrating that loss of AF mechanical integrity precedes clinically detectable degeneration. Pathological dScoli tissue showed the greatest mechanical reductions, while IVDD properties overlapped substantially with those of Older Asymptomatic tissue, suggesting that aging alone can bring the AF to a mechanically vulnerable state resembling early disease. Western blot analysis showed that MMP-3 abundance rose significantly with age in asymptomatic tissue but continued to rise progressively in IVDD, indicating divergent regulated versus dysregulated proteolytic trajectories in aging versus disease. HTRA1 was constitutively expressed across all groups with no significant age or pathology effect. Critically, global correlation analysis identified a significant inverse relationship between MMP-3 expression and peel stiffness across all groups (R = -0.37, p = 0.026), providing the first direct quantitative evidence in human AF tissue linking proteinase activity to reduced interlamellar mechanical integrity. IHC validated these findings and revealed a more diffuse spatial distribution of MMP-3 in dScoli tissue compared to the localized pattern in asymptomatic and IVDD specimens, while confirming proteoglycan presence within the AF as a structural substrate for MMP-3-mediated degradation. Together, these findings identify the ILM as an early, mechanically vulnerable site of age-related AF deterioration that precedes nucleus pulposus-centric degenerative changes, and establish MMP-3 as a mechanistically plausible biomarker linking proteolytic remodeling to interlamellar mechanical failure. This work provides a foundation for future investigation of active enzyme activity, lamellar-specific mechanics, and targeted interventions aimed at preserving AF integrity before the onset of overt, symptomatic disc disease.

Name thesis:degree_name

Master of Science (MSc)

Discipline thesis:degree_discipline

Engineering – Biomedical

Grantor dc:publisher.institution

Graduate Studies

Year dc:date.issued

2026

Author dc:creator

• Salaam, Mohammed

Advisors dc:contributor.advisor

• Swamy, Ganesh
• Duncan, Neil

Committee members dc:contributor.committeemember

• Hart, David
• Salo, Paul

• spine
• biomechanics
• human tissue
• Proteinase

Statement dc:rights

• University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.

Language dc:language.iso

en

DOI

https://dx.doi.org/10.11575/PRISM/51702

OAI identifier oai:identifier

oai:ucalgary.scholaris.ca:1880/125444